What Could Be Failing? Garbled Screen, Late iMac 2009

Hi. This morning, the iMac's screen went garbled. When I restarted it and repaired the permissions and repaired the disk using Disk Utility, it seems to be ok now. I checked the hardisk on Bootcamp using Speedfan, it's fine, no errors.

What could be failing? Is it software related (OS X 10.9.2 is installed) or hardware relatedIt also says Verified on Disk Utility. That could be failing? Is it software related (OS X 10.9.2 is installed) or hardware related?

The screen looked like these:

Thank you in advance. Have a great holy week & a advanced happy Easter.

God bless, Rev. 21:4, Matt. 16:18, Cor. 13